The Biased Ideal Rectifier

T HE concept of an ideal rectifier gives a useful approximation for the analysis of many kinds of communication circuits. An ideal rectifier conducts in only one direction, and by use of a suitable bias may have the critical value of input separating non-conduction from conduction shifted to any arbitrary value, as illustrated in Fig. 1. A curve similar to Fig. 1 might represent for example the current versus voltage relation of a biased diode. By superposing appropriate rectifying and linear characteristics with different conducting directions and values of bias, we m a y approximate the characteristic of an ideal limiter, Fig. 2, which gives constant response when the input voltage falls outside a given range. Such a curve might approximate the relationship between flux and magnetizing force in certain ferromagnetic materials, or the o u t p u t current versus signal voltage in a negative-feedback amplifier. The abrupt transitions from non-conducting to conducting regions shown are not realizable in physical circuits, but the actual characteristics obtained in many devices are much sharper than can be represented adequately by a small number of terms in a power series or in fact by any very simple analytic function expressible in a reasonably small number of terms valid for both the non-conducting and conducting regions. In the typical communication problem the input is a signal which may be expressed in terms of one or more sinusoidal components. The output of the rectifier consists of modified segments of the original resultant of the individual components separated by regions in which the wave is zero or constant.